Brake shoe centering mechanism

ABSTRACT

A brake in which friction between a rotating drum and a primary brake shoe produces a force which acts on a secondary brake shoe to move the latter shoe into engagement with the drum to thereby decelerate the drum. A shoe retracting device is mounted on the brake backing plate for operative engagement with a strut which interconnects a pair of adjacent ends of the primary and secondary shoes so that the secondary shoe is withdrawn from engagement with the drum upon brake release.

United States Patent 1191 Winge [54] BRAKE SHOE CENTERING MECHANISM [75]Inventor: John L. Winge, South Bend, Ind.

[73] Assignee: The Bendix Corporation, South Bend, 1nd.

221 Filed: June 16,1971

[21] Appl.No.: 153,717

[52] US. Cl. ..,...188/216,188/79.5 P, 188/331 [51] Int. Cl ..Fl6d 65/16[58] Field of Search ..l88/79.5 P, 196 M, 216, 331

[56] References Cited UNITED STATES PATENTS 2,084,972 6/1937 Irving..l88/79.5P 2,152,041 3/1939 Goepfrich ..188/79.5P

[111 3,724,61 l 1451 Apr. 3, 1973 8/1939 Burnett ..188/331 6/1965 Price..188/79.5PX

'Printary Examiner-Duane A. Reger At't0rney--Wi1liam N. Antonis et a1.

511 ABSTRACT A brake in which friction between a rotating drum and aprimary brake shoe produces a force which acts on a secondary brake shoeto move the latter shoe into engagement with the drum to therebydecelerate the drum A shoe retracting device is mounted on the brakebacking plate for operative engagement with a strut which interconnectsa pair of adjacent ends of the primary and secondary shoes so that thesecondary shoe is withdrawn from engagement with the drum upon brakerelease.

PATENn-jmm 197s 3124,61 l

INVENTOR. dOHN L. W/NGE ATTORNEYS BRAKE SHOE CENTERING'MECHANISMBACKGROUND OF THE INVENTION The brake mechanism herein disclosed relatesspecifically to automotive drum brakes which have been competitivelychallenged by disc brakes in recent years.

In order to meet this challenge, various improvements to drum brakeeffectiveness have been offered, such for example, as changing liningcompositionto provide better drum retardation and longer lining life.

Such innovations, while accomplishing their intended goal, sometimescreate other problems which must be resolved to make the improvementpractical. The use of improved lining composition, forexample,'intensifies a condition known in the brake art as secondarybrake shoe drag. This condition is particularly troublesome with acertain type of drum brake which when applied urges the primary shoe offits anchor memberinto engagement with the brake drum imparting itsrotational action thereto'and to one end of the secondary shoe, throughthe interconnecting strut,forcing the other end of said secondary shoeagainst the anchor member. When the brake is released, a spring pullsthe primary shoe end into contact with the anchor member, thus removingthe primary shoe from frictional contact with the drum. As to thesecondary shoe, it is already against the anchor member and because ofits tendency, due to self-energization, to remain in contact with thedrum after brake release, coupled with the fact that there is frictionalresistance between the secondary shoe and backing plate opposingmovement of the secondary shoe, there is noguarantee that the secondaryshoe will be retracted from the drum. Various ways of combatingsecondary shoe drag have been proposed, such as shown in US. Pat. Nos.3,175,644 and 3,189,131, assigned to the common assignee for thisinvention. The prior art approach to the problem, as analyzed by thisapplicant, has been too complicated, hence too expensive, and/orinadequate from the standpoint of not doing the job effectively. Thepresent invention is believed to solve many of the problems heretoforepreventing the adoption of such a device for general use. i

I SUMMARY OF THE INVENTION The principal object of the invention is toprovide a brake shoe retracting device which maintains a constant forceirrespective of shoe wear.

, Another object of theinvention is to provide a device capable ofeffectively centering the shoes after each brake release regardless ofthe amount of the adjust- DESCRIPTION OF THE DRAWINGS FIG. 1 is avertical section of the brake taken just inside the drum head, andembodying the principles of my invention;

FIG. 2 is a partial section taken on theline 2-2 of FIG.1;

FIG. 3 is a section through the lower end of the brake taken on the line3-3 of FIG. 1;

FIG. 4 is a section corresponding to FIG. 2, illustrating the action ofthe retracting device;

FIG. 5 is a perspective view of the collet which forms a part of theinvention.

DETAIL DESCRIPTION Referring now to FIG. 1, the brake with which thedevice of my invention is associated comprises a backing plate 10secured to an appropriate portion of the vehicle, such as an axleflange, not shown, by bolts 12, passing through holes 14 of the backingplate 1 0. Brake shoes 16 and 18 are slidably mounted on'the backingplate 10 so that webs 20 and 22, respectively, of the shoes are inpivotal engagement at their upper adjacentends with anchor member 24attached to the backing plate 10. Linings 17 and Hate suitably attachedto the shoes 16 and 18, respectively. A shoe web guide elenient 26 isfastened to the anchor member '24 to slidably receive a pair of upperadjacent ends 28 and 30 of the shoes 16 and 18, thereby locating theshoe ends in a fixed lateral position with respect to the backingplate.The shoes 16 and 18 are interconnected at their lower adjacent ends 32and 34, respectively, by a strut 36. The strut 36, which is of theadjustable type, comprises an adjusting screw 38, a socket member 40,

non-rotatably engaging the shoe end 34, and a nutmember 42 non-rotatablyengaging the shoe end 32. The adjusting screw 38, which threadedlyengages the nut member 42 and freely rotates'within the socket member40, is provided with a ratchet wheel 44 to be engaged by a tool insertedthrough opening 46 in the backing plate 10 when a brake shoe adjustmentis desired. The adjustable strut 36 is of conventional construction andwell known to persons skilled in the art. Means such as a spring 48draws the pair of adjacent shoe ends 32 and 34 into engagement with thestrut parts 42 and 40, respectively, thereby retaining :the strut partsin assembled relationship.ln released position, the upper adjacent shoeends are held against the anchor member 24 by springs 50 and 52connected, respectively, at one end to the shoe ends 28 and 39 and tothe anchor member 24 at their opposite ends. The shoes 16 and 18 areyieldingly retained in slidingil'olationship to the backing plate 10byhold-down springs 54. The adjacent shoe ends 28 and 30 are spreadapartfrom the anchor member 24 into engagementwitha rotatable drum 56,secured to a vehicle wheel, not

shown, by a fluid motor 58, mounted tothe' backing The shoe positioningmeans 66 to which this invention relates comprises a bracket 68 ofU-shaped construction suitably secured to the backing plate 10, as bywelding transverse section 70 thereto. Parallel spaced sides 72 and 74,integrally related to the transverse section 70, extend generally atright angles to the backing plate and forwardly thereof, as best shownin FIG. 3. The forward ends of the sides 72 and 74 are formed withopposed slots or notches 76 and 78 through which the strut 36 slidesduring brake application and release, as the fluid motor 58 ispressurized and depressurized, in a manner well known to those personsskilled in the art. The shoes 16 and 18 are biased to a releasedposition by a preloaded coil spring 80 interposed between the spacedparallel sides 72 and 74 of the bracket 68. The convolutions of the coilspring 80 circumscribe the nut member 42 of the strut 36. A washer 81 ispositioned between one end of the spring 80 and the side 74. A collet 82is located coaxially of the nut member 42 and is equipped with anintegral flange 84 engageable by the other end of the coil spring 80which urges the flange 84 against the side 72. The collet 82 is furtherprovided with an axial extending skirt 86 having longitudinal slots 88,dividing the skirt into fingers or sections 90. The design of the skirt86 with respect to its frictional engagement of the nut member 42 issuch that a sliding frictional fit is obtained on the nut which willsustain the load of the coil spring 80 during forward braking, directionof arrow FIG. 1, but will slide during reverse braking if there isclearance between the drum and the shoe 16. That is, the frictionalforce between the skirt 86 and the nut 42 is set' at a predeterminedvalue which is greater than the biasing force of the preloaded coilspring 80, so that the collet 82 and nut 42 will move as a unit inestablishing the shoes in their proper relationship to the drum duringforward braking, assuming the lining 19 is properly adjusted to thedrum. However, on reverse braking at a time when there is clearancebetween the lining 17 and the drum, any braking force acting on the shoe16 through said strut in excess of said predetermined value will causerelative movement between the strut and collet. This will slide thestrut to the left in the collet, thus causing the nut 42 to assume a newposition in the collet.

MODE OF OPERATION For forward movement of the vehicle, assume drumrotation is in the direction of the arrow of FIG. 1. Pressurization ofthe fluid motor 58 with drum rotation as shown forces the end 28 of theshoe 16 away from the anchor 24 causing the lining 17 to frictionallycontact the drum 56. This frictional contact between lining and drumtends to rotate theshoe 16, which is the primary shoe in forwardbraking, in a counterclockwise direction. Concurrently, withcounterclockwise movement of the shoe 16 as aforesaid, the shoe 18,which is the secondary shoe in forward braking, through contact of thelining 19 with the drum 56, also tends to be rotated counterclockwise,thus driving the end 30 of the shoe 18 against the anchor member 24.This action of the rotating drum on the shoe 18 urging it against theanchor 24 is enhanced or intensified by the rotational movement of theshoe 16, drivably connected to the shoe 18 through the strut 36.Releasing the pressure from the wheel cylinder 58 permits the spring 50to draw the end 28 of the shoe 16 against the anchor member 24 while atthe same time withdrawing the lining 17 from contact with the inner drumsurface through pivotation of the shoe end 32 on the end of the nut 42.Now, as to the shoe 18, which as aforementioned is the secondary shoe inforward braking, it will be remembered that this shoe is already inabutment with the anchor member 24 and due to its self-energizetion, ithas a tendency to remain in contact with the drum and would probablyremain in contact until knocked loose, if it were not for applicantsretracting device 66 which effectively withdraws the secondary shoe fromthe drum upon brake release.

It will be recalled that pressurization of the fluid motor 58 caused theshoes to engage the rotating drum, thus tending to rotate both shoescounterclockwise. This rotational action moved the strut 36 and collet82 to the right an amount A, determined by the distance between thebrake lining 19 and the drum, at the same time, compressing the spring80, as best shown in FIG. 4. Releasing the pressure from the wheelcylinder 58 permits the spring 50 to return the shoe end 28 to theanchor 24 and also enables the preloaded spring to return the strut 36to the position of FIG. 1, at the same time disengaging the lining 19 ofthe shoe 18 from the drum. This action of the spring 80 in disengagingthe secondary shoe 18 from the drum is through the spring 48 which tiesthe adjacent ends 32 and 34 of the respective shoes to the adjustablestrut. This provides for a positive withdrawal of the secondary shoe 18after each forward brake application, thus increasing lining life.

As the linings 17 and 19 wear, adjustment may be made by inserting atool through the opening 46 and rotating the ratchet wheel 44. Upon theinitial forward and reverse brake applications after making theadjustment, the shoes will acquire their respective positions inrelationship to the drum. On reverse braking, the strut 36 and moreparticularly the nut 42 will move to the left if there is clearancebetween the shoe [6 and the drum, thus sliding the nut in the colletsince the flange 84 is now abutting the side 72. This, of course, meansthat as the lining 17 wears and adjustments are made, the nut 42 slidesthrough the collet to the left taking on new positions in the collet.Although the strut is shown for manual adjustment, applicants devicefunctions equally well with automatic adjustment.

While there have been described above the principles of this inventionin connection with a specific device, it is to be understood that thisdescription is made only by way of example and not as a limitation tothe scope of the invention.

I claim:

1. A drum brake which comprises:

a backing plate;

a pair of brake shoes slidably mounted on said backing plate, said shoesarranged on said backing plate to have two pairs of adjacent ends;

a strut interconnecting one pair of adjacent ends of said shoes;

means for retaining said one pair of adjacent ends of said shoes inengagement with said strut;

an anchor member carried by said backing plate about which the otherpair of adjacent ends of said shoes pivot;

means for positioning said shoes with respect to said drum to establisha predetermined relationship between the drum and the respective shoesupon brake release; said last named means including a bracket secured tothe backing plate, said bracket having parallel spaced sides withopposed slots therein; and preloaded spring means operatively connectingsaid strut to said bracket, said strut freely sliding in said slots assaid shoes are positioned under the influence of said preloaded springmeans so that the biasing force acting to return said shoes to theirbrake release position remains constant. 2. The structure, as recited inclaim 1, wherein said preloaded spring means includes a coil springpreloaded between said parallel sides.

3. The structure, as recited in claim 2, which further includes a colletfrictionally engaging said strut and located at one end of said coilspring, and a washer located at the other end of said coil spring.

4. The structure, as recited in claim 3, wherein said collet, saidwasher and said coil spring are coaxially arranged on said strut betweensaid parallel sides.

v5. The structure, as recited in claim 4, wherein said strut isadjustably positioned in said collet.

6. The structure, as recited in claim 5, wherein the frictional force ofengagement between said collet and strut resisting relative motiontherebetween is of a predetermined value which is greater than the forceof the preload on said coil spring.

1. A drum brake which comprises: a backing plate; a pair of brake shoesslidably mounted on said backing plate, said shoes arranged on saidbacking plate to have two pairs of adjacent ends; a strutinterconnecting one pair of adjacent ends of said shoes; means forretaining said one pair of adjacent ends of said shoes in engagementwith said strut; an anchor member carried by said backing plate aboutwhich the other pair of adjacent ends of said shoes pivot; means forpositioning said shoes with respect to said drum to establish apredetermined relationship between the drum and the respective shoesupon brake release; said last named means including a bracket secured tothe backing plate, said bracket having parallel spaced sides withopposed slots therein; and preloaded spring means operatively connectingsaid strut to said bracket, said strut freely sliding in said slots assaid shoes are positioned under the influence of said preloaded springmeans so that the biasing force acting to return said shoes to theirbrake release position remains constant.
 2. The structure, as recited inclaim 1, wherein said preloaded spring means includes a coil springpreloaded between said parallel sides.
 3. The structure, as recited inclaim 2, which further includes a collet frictionally engaging saidstrut and located at one end of said coil spring, and a washer locatedat the other end of said coil spring.
 4. The structure, as recited inclaim 3, wherein said collet, said washer and said coil spring arecoaxially arranged on said strut between said parallel sides.
 5. Thestructure, as recited in claim 4, wherein said strut is adjustablypositioned in said collet.
 6. The structure, as recited in claim 5,wherein the frictional force of engagement between said collet and strutresisting relative motion therebetween is of a predetermined value whichis greater than the force of the preload on said coil spring.